Centering tool for drilling

[kooldino]

So unfortunately, I'll sometimes encounter situations where I need to drill out a bolt. I use a punch and try to center things the best I can, but it usually doesn't end up dead center.

Is there some kind of centering tool or some kind of trick I could use to make sure I start drilling dead center on the broken bolt?

I had a thought of using some sort of "sleeve" to go around the bolt and using the largest bit I could fit inside of the sleeve to start the hole. This way, the tip would cut in and should give me a good center hole. Of course, that's easier said than done.

Any other suggestions?

 

[buffalobill]

many times, i have been frustrated trying the same thing you are doing, with a center punch. unfortunately, it seems like the best solution would be to somehow "even the face" of the broken bolt or stud that you are drilling. on any broken bolts that i have dealt with, they leave an uneven face, along with a small ridge where they broke. if there was a convenient way to flatten that, i think the center punch method would work much better. maybe a very small milling bit, to make it flat?

 

[Jim Johnstone]

many times, i have been frustrated trying the same thing you are doing, with a center punch. unfortunately, it seems like the best solution would be to somehow "even the face" of the broken bolt or stud that you are drilling. on any broken bolts that i have dealt with, they leave an uneven face, along with a small ridge where they broke. if there was a convenient way to flatten that, i think the center punch method would work much better. maybe a very small milling bit, to make it flat?

Unless you can put it in an actually milling machine, I don't think an end mill will help. I'd use a die grinder to try to face the broken bolt as best as possible, then center punch, then use a center drill, then use a left handed drill and hope it lets go and spins out.

 

[kooldino]

many times, i have been frustrated trying the same thing you are doing, with a center punch. unfortunately, it seems like the best solution would be to somehow "even the face" of the broken bolt or stud that you are drilling. on any broken bolts that i have dealt with, they leave an uneven face, along with a small ridge where they broke. if there was a convenient way to flatten that, i think the center punch method would work much better. maybe a very small milling bit, to make it flat?

That will only work in some cases. All too often, the broken fastener is flush with the flange it broke in.

 

[royesses]

Maybe this?
http://www.boltmasterusa.com/products.htm

 

[djjsr]

Whenever I need to drill something with a bit of precision, I'll use a countersink to start. It's got a sharp point and is less likely to wander. Once the hole is started, switch to a drill bit and the countersink will locate it.

I have a few different sizes, similar to this ............

 

[pro machine Engineering]

if able grind the top of bolt flat with the top of the part. Using a compass or dividers set at half the diameter of the bolt. Set one point on the line betweeen the part and the bolt and swing an arc with the other point on the bolt do this 3 or 4 places around the bolt. Where the arcs meet on the bolt will be the center. Center punch and drill

 

[Punkinhead]

Center drills are used to start a hole because they're short, not flexible, tend not to wander, and leave a slight countersink for a drill bit to follow. They're meant to be used in a drill press or milling machine, but I've had success using them in a hand held drill also.

Any place that sells machine shop supplies has them (MSC, Enco, Grizzly, etc) Here's an example of cheap import ones which work fine: center drills

 

[tcsalvage]

also remember that the thread at the end of the broken fastener will throw you off, so allow for the end of the thread, center punch, center drill and drill tap size hole through the bolt. you should be able to pick the threads out or carefully tap the hole.

 

[lilredex]

Make a drill guide. If the stud protrudes, all the better. Drill the stud size in a short strap, then drill the center drill size in another piece, weld the two together with the holes concentric. If you have a mill, you can save a step and use one piece. If the stud is flush you need to hold the guide, you made, in place by using existing, adjacent bolts.

Center punching is not always a guarantee the bit won't walk.........your guide will, if made and retained properly. Once you get a good pilot started, use those LH bits suggested. If you don't have LH bits, get some, you'll use them.

 

[JASTECH]

Very good suggestions above. What grade is the bolt? That will help dictate the drill bit hardness needed. For very hard steel I use CRYOBIT with their spray lube. Also, if drilling by hand held drill the a support of some sort will be needed to maintain the same angle as the bolt.

Thanks, JASTECH

 

[Hammer1963]

Grind the stud flat if possible and use a transfer punch the same diameter as the broken stud/bolt. This will help you get a more accurate center. Then use a center punch and follow up with a center drill. Works for me.